const a = { val: 'a' }
const b = { val: 'b' }
const c = { val: 'c' }
const d = { val: 'd' }

a.next = b
b.next = c
c.next = d



// 遍历链表
let p = a;
while (p) {
    console.log(p.val)
    p = p.next;
}

// 插入
const e = { val: 'e' }
c.next=e
e.next=d

// 删除
c.next=d